Download The Fossil Record

Evolution
I. Evidence
II. Populations & Gene Pools
III. Forces of Evolution
IV. Natural Selection
V. Forms of Selection
VI. Adaptation
The Fossil Record
Evidence for Evolution
The Fossil Record – Dating Fossils
13.4 The study of fossils provides strong evidence for
evolution
Dating fossils
Relative dating – old layers under new
Absolute dating – radioactive decay
ƒ Many fossils link early extinct species with species living
today
– A series of fossils documents the evolution of whales
from a group of land mammals
Half-Life examples
U-238 Æ 4.5 billion years
C-14 Æ 5730 years
K-40 Æ 1.25 billion years
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Whale Evolution
Pakicetus
A Brief History of Life
Pakicetus (terrestrial)
lived on land
skull had whale
characteristics
Rodhocetus kasrani
reduced hind limbs
could not walk;
swam with up-down motion like
modern whales
Rhodocetus (predominantly aquatic)
Pelvis and
hind limb
Pelvis and
hind limb
Dorudon (fully aquatic)
Balaena (recent whale ancestor)
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Fossil Record: Balance between new species & extinction
Number of families
History of Life – the last 1.5 million years
800
600
400
200
0
600
Cambrian
(545-490)
500
400
Silurian
(438-408)
Ordovician
(490-438)
300
200
0
100
Carboniferous Triassic Cretaceous
(360-280)
(248-213) (144-65)
Devonian
(408-360)
Permian Jurassic
(280-248) (213-144)
Tertiary
(65-2)
Millions of years ago
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Central Theme of Evolution
Descent with modification from a common ancestry
Evidence from
Comparative Anatomy
Homologous Structures
Vestigial Structures
Embryonic Development
13.5 Evidence for the evolutionary view of life
ƒ Comparative anatomy is the comparison of body
structures in different species
ƒ Homology is the similarity in characteristics that result
from common ancestry
– Vertebrate forelimbs
Molecular Genetics
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The Anatomical Record
Homology in vertebrate forelimbs
structures with different appearances and functions
that all derived from a common ancestor
The Anatomical Record
Vestigial structures
organs with no apparent modern function,
but resemble ancestral structures
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Comparative Development
Molecular Biology - Reveals evolutionary relationships
Genetic variation in pine DNA
Western white pine
Molecular Biology - Reveals evolutionary relationships
Molecular Phylogeny
DNA and the
Hemoglobin
Gene
4
Gene Pools, Alleles and Allele Frequency
Genes within Populations
Gene pool: All the possible alleles for a particular
gene (or all the genes) within a given population
I. Gene Pools & Microevolution
II. Causes of Evolutionary Change
III. Natural Selection
IV. Forms of Selection
V. Adaptation
Allele Allele
B
b
Number of 150
50
alleles
Gene Pool 200 alleles
Allele
frequency
Gene Pools & the Hardy-Weinberg Principle
Parental Population
p = dominant allele frequency
q = recessive allele frequency
p+q=1
(p + q)2 = p2 + 2pq + q2
Offspring
Genotype frequencies
calculated from allele frequencies
p2
Homozygous
Dominant
+
2pq
Heterozygous
+
q2
0.75
0.25
13.10 CONNECTION: The Hardy-Weinberg
equation is useful in public health science
ƒ The frequency of individuals with cystic fibrosis is
approximately q2 = 1/3300 = 0.0003
– The frequency of the recessive allele is
q = .0174 or 1.7%
–
ƒ The frequency of heterozygous carriers of cystic fibrosis is
2pq = 2 x 0.983 x 0.017 = 0.034
ƒ Around 3.4% of Caucasian Americans are carriers for cystic
fibrosis
Homozygous
Recessive
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5
Hardy-Weinberg Principle
• p2 + 2pq + q2 = 1
p = dominant allele frequency
q = recessive allele frequency
• allele and genotype frequencies in a population:
– will remain constant over time
– No evolution
= equilibrium population
Assumptions of the Hardy-Weinberg Principle
Under several assumptions, evolution will not occur
i.e., Allele frequencies will not change
1. no mutation
2. no gene flow (no immigration/emigration)
3. large population size (no genetic drift)
4. random mating
5. no natural selection
If these assumptions are met, sexual reproduction alone
will not change allele frequencies in the population
Forces of Evolution
Microevolution will occur
… Allele frequencies will change if
1. mutation
2. gene flow (no immigration/emigration)
3. no genetic drift
4. nonrandom mating
5. natural selection
Forces of Evolution – Mutation
DNA Mutations
Point mutations alter a single base.
Base substitution, Insertion or Deletion
Chromosome mutations
Deletions – part of chromosome is lost
Duplication – part of chromosome is copied
Inversion – part of chromosome in reverse order
Translocation – part of chromosome moved to new location
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Mutation Frequency
How often? 1 in 100,000 cell divisions
1 in 50 million base pairs
1 in a million gametes
Bacterial genome ≈ 5000 genes
X 200 bacteria = 1,000,000 genes per 200 bacteria
Mutation and sexual reproduction produce genetic
variation, making evolution possible
ƒ Mutation, or changes in the nucleotide sequence
of DNA, is the ultimate source of new alleles
– Occasionally, mutant alleles improve the adaptation of an
individual to its environment and increase its survival and
reproductive success (for example, DDT resistance in insects)
1 mutation in every 1,000,000 genes
1 teaspoon of soil ≈ 1 billion bacteria
1 billion bacteria ÷ 200 bacteria/1 mutation =
5 million mutations in 1 teaspoon of soil
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Forces of Evolution – Gene Flow
•
Gene flow = migration between populations
•
•
–
–
populations exchange genetic material
can change allele frequencies by altering the gene pool
Other examples of gene flow
1. Bacterial transformation from plasmid transfer
2. Virus and plasmid vectors in recombinant DNA technology
3. People
Forces of Evolution – Genetic Drift
Æ Frequencies of particular alleles
change by chance alone.
Northern elephant seal
1920 ~ 20 animals
2007 ~ 130,000 animals
A. Population bottlenecks
Populations reduced to small # then recover
Genetic bottleneck results in
Loss of genetic variation
Reduced capacity to evolve
Founders
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Genetic drift in small populations
Forces of Evolution – Non-Random Mating
Æ Frequencies of particular alleles change by chance alone.
• important in small populations, but less important in
large populations
Mating of phenotypically similar individuals
Positive Assortative mating
Inbreeding
Increases proportions of homozygotes
Decreases phenotypic variation
Greater Prairie Chicken
Cheetah
Negative Assortative mating
Increases phenotypic variation
–Natural Selection &
–DARWIN’S THEORY OF EVOLUTION
Charles Darwin and Natural Selection
The voyage of the Beagle (1831–1836). The insets show a young
Charles Darwin and his ship.
– In 1859, Darwin published On the Origin of Species by
Means of Natural Selection, presenting a strong, logical
explanation of evolution by natural selection
North
America
Great
Britain
Europe
Asia
ATLANTIC
OCEAN
PACIFIC
OCEAN
Africa
PACIFIC
OCEAN
Equator
The
Galápagos
Islands
PACIFIC
OCEAN
Pinta
South
America
Genovesa
Australia
Marchena
Equator
Pinzón
Fernandina
0
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40 km
Cape of
Good Hope
Tasmania
Isabela
0
Daphne
Islands
Andes
Santiago
Santa
Santa
Cruz
Fe
Florenza
Cape Horn
San
Cristobal
New
Zealand
Tierra del Fuego
Española
40 miles
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13.2 Darwin proposed natural selection as the
mechanism of evolution
13.2 Darwin proposed natural selection as the
mechanism of evolution
ƒ Darwin observed that
– Organisms vary in many traits
ƒ Darwin reasoned that traits that increase their chance
of surviving and reproducing in their environment
tend to leave more offspring than others
– Organisms produce more offspring than
the environment can support
ƒ As a result, favorable traits accumulate in a
population over generations
ƒ Descent with modification is the consequence of
Natural Selection
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Charles Darwin, 1859:
On the Origin of the Species
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Natural Selection and
Adaptation
Peppered Moths
Charles Darwin proposed
Natural Selection as the
mechanism of evolution
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Peppered Moths and Industrialized Melanism
Types of Natural Selection
• Æ The second half of the twentieth century saw
widespread implementation of pollution controls, thus
trends appear to be reversing and light colored moths may
again dominate.
VI. Adaptation
Measures of Fitness in Natural Selection
• Fitness Criteria
• 1. Survival to reproductive maturity
• 2. Passing genes to the next generation.
• Natural Selection favors phenotypes with the
greatest fitness.
Camouflage –
a result of
natural
selection
Flower mantid
Leaf mantid in Costa Rica
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Artificial Selection
• Darwin found convincing evidence for his ideas
in the results of artificial selection
• Selective breeding of plants and animals
Speciation – Formation of New Species
A. Driven by Isolation of members of a species.
B. Types of Isolation
1. Pre-zygotic
1. Geographic
2. Temporal
3. Ecological
4. Behavioral
5. Mechanical
2. Post-zygotic
1. Failure to develop
2. Sterile offspring
Artificial
Selection
Ancestral dog (wolf)
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Speciation of geographically isolated
antelope squirrels
A. harrisi
South
Mechanical Isolation in Snails
A. leucurus
North
Genital Openings
11
Reduced Hybrid Fertility
Darwin’s Finches & Divergent Evolution
46
END Evolution
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